If $3a + 9b = 1$ and $8x + y + 3z = 8$, what is $48x - 45b + 18z + 6y - 15a$ ?
$= -15a - 45b + 48x + 6y + 18z$ $= (-5) \cdot (3a + 9b) + (6) \cdot (8x + y + 3z)$ $= (-5) \cdot (1) + (6) \cdot (8)$ $= -5 + 48$ $= 43$